Not everyone reacts to optical illusions equally: some are completely fooled by them, while others just can't see what all the fuss is about. It depends on the size of your visual cortex...and that can determine how introspective you are.

Specifically, the amount of gray matter in the visual cortex goes a long way to determining how much a person is able to process and solve optical illusions, a fact that was discovered last year by researchers at University College London. They then decided to take things a step further by looking for other parts of the brain that correlate with the size of the visual cortex.

With the help of 30 volunteers and an MRI scanner, they discovered an unlikely relationship between the visual cortex and another structure at the front of the brain: the anterior prefrontal cortex, or aPFC. The relationship is inverse - the bigger visual cortex you have, the smaller your aPFC is, and vice versa. Previous studies have linked the aPFC with introspection, as people with more gray matter in that particular area are better able to evaluate if they've done the right thing or made a smart decision.

The researchers speculate that those with a higher level of introspection are less able to deal with the more complex aspects of visual perception, and they hope to put that to the test soon in behavioral studies. Team member Chen Song suggests that the reason for this trade-off is that the two areas are located on the respective far ends of the brain's anterior-posterior axis, and research into animal brains has already found that genes tend to be more heavily expressed on one side or the other along this axis.

That said, at least one researcher thinks that those with the more developed visual cortex and the smaller aPFC got the better deal. Elliott Freeman of City University London suggests:

"But bigger is not necessarily better in terms of brain power. It might be better to have fewer synaptic connections for more focused and coherent decision making. A brain with more visual volume and less frontal volume might actually work better."

It's a good point, but just to be sure, I think we ought to double-check Freeman's brain, preferably with a barrage of optical illusions. After all, that's just what a non-introspective, high-visual brain person would say. Oh dear...I seem to have accidentally invented a whole new type of prejudice. Sorry about that, everyone.